Call-only ads are designed to result in calls made directly from Google's search result page, as opposed to search or display ads, where the ad impression results in a click. Same goes for call-only extensions, as they offer the same click-to-call functionality for call-ready devices (e.g. smartphones).
While ClickGUARD can track and process ad clicks, the system cannot track calls, as the data available upon clicks (e.g. IP address) is not obtainable during phone calls. Without actionable data, the system is unable to perform campaign optimisations. Therefore ClickGUARD"s optimisation tools do not support call-only ads and extensions.